The invention relates to transparent substrates, in particular those made of an inorganic rigid material such as glass or of an organic material of the rigid, semi-rigid or flexible polymer type, of the polycarbonate, polymethyl methacrylate PMMA and polyethylene terephthalate PET type, the said substrates being coated with a stack of thin layers comprising at least one layer exhibiting metal-type behaviour which can act on solar radiation and/or on long-wavelength infrared radiation.
The invention relates more particularly to the use of such substrates for manufacturing thermally insulating and/or anti-UV windows. These windows are intended to equip both buildings and vehicles, for the purpose, in particular, of decreasing the air-conditioning load and/or of reducing excessive over-heating caused by the ever increasing extent of glazed surfaces in the passenger compartments.
A known type of multilayer stack for giving the substrates such properties consists of at least one metallic layer, such as a silver layer, which is arranged between two layers of dielectric material. This stack is generally obtained by a succession of depositions carried out using a vacuum technique, such as sputtering, optionally assisted by a magnetic field.
Patent EP-0,638,528 thus discloses a glazing assembly, more particularly a multiple glazing assembly of the double-glazing type intended for buildings, in which at least one of the glass substrates which compose it includes a stack of thin layers consisting of two silver layers inserted between three coatings of dielectric material. According to this document, the first silver layer, that is to say that which is closest to the substrate carrying the stack, is chosen to be thinner than the second, in particular so that its thickness corresponds to approximately 65% of the thickness of the second silver layer. This "dissymmetry" in the thickness of the two functional layers of the stack has proved to be advantageous in that it makes it possible to obtain glazing assemblies having a satisfactory selectivity, if the selectivity S is defined as the ratio of the light transmission T.sub.L to the solar factor SF (which is itself defined by the ratio between the total energy entering the room through the glazing in question and the incident solar energy). Furthermore, this dissymmetry makes it possible to obtain glazing assemblies whose visual appearance in reflection is attractive, in particular by having an agreeable colour, in the blues or the blue-greens, but very neutral, very "white-washed".
However, the type of multilayer stack recommended in this document is capable of further improvement, very particularly with regard to its thermal performance characteristics. Thus, the glazing assemblies described have at best a value of the solar factor SF of 38%, while in the future it is intended to manufacture glazing assemblies whose solar factor can be lowered to values which are less than or equal to 32% and even less than or equal to 30%.